Heat Pumps and Electric Heating - heat pump question (I think its bad)

I have a heat pump system and its seems to put out warm air.
when I switch it over to AC side, it just blows warm air.
I go outside and the unit outside is not doing anything.
fan is not moving. I went to check to make sure the breaker is on for the AC and its tripped off. I switch it on and it immediatly trips off again.
The house has been sitting empty for 1-2 years.
house was built in 1990.

questions:
1. what may be wrong and what is most probably wrong?
2. can I fix it? (can I just replace the outside unit) or is this a pro job only?
3. will it heat over the winter?
4. Estimated cost to fix/replace?
5. What are the better manufacterers?

I'm not a HVAC guy but have a few suggestions:

With the breaker off, inspect all the wiring going to the outside compressor. It is likely that an animal or weed eater might have damaged the wiring going to the unit.

Yeah it's shorting out somewhere, follow the wires and check for loose connections and melted wire insulation, as best as ya can.

Power off, remove the service panel. Check all the wires inside the unit, and also look for bugs or what not under the contactor points on the contactor.

had an HCAV pro come out and look at the unit today.
he said a coil in the outside unit is stuck open.
he recommends replacing the unit.
a SEER 13 system can use the same air handler inside the house.
So basically its a 3K job to make the system work again.
everything will be new outside, a new coil on the inside along with a new tstat and a few other minor replacements.

had an HCAV pro come out and look at the unit today.
he said a coil in the outside unit is stuck open.
he recommends replacing the unit.
a SEER 13 system can use the same air handler inside the house.
So basically its a 3K job to make the system work again.
everything will be new outside, a new coil on the inside along with a new tstat and a few other minor replacements.

hummm...

I suggest a second opinion.

IMO

There are only 2 coild in a heat pump unit outside. 1 is the contactor coil and the other is the reversing valve. If either of these were stuck open it would not cause your breaker to trip. If it's sat for 2+ years the compressor could be stuck. I too would get a 2nd opinion.

perhaps my wording is not precise.
the coil on the inside beeing replaced with the outside unit so that they work properly is correct.

the outside unit he said,
has 2 of whatever is bad. 1 to start the unit, another to run the unit. One of those is bad, and stuck open. something about if the unit gets to hot it opens and turns the unit off.

mattison, what you said sounds about right.

Sounds more like he is referring to a capacitor. Easy replacment to rule it out.

I asked about the cap's.
he said its not those.

perhaps he said one of the windings is bad?

If he said windings then it's shot.

thanks for all the help guys/gals.